Tcp connection troubles on ubuntu after vmware conversion

We had an old vmware server on a 2008 server, this has 3 virtual machines. One I installed and two that were installed before i was here.
We converted these a few weeks ago to esxi 5.0.

Since then we seem to have some issues on two of the three ubuntu vm's (the one I installed works correctly).

Network is up and i have a constant ping open from and to machine.207 (one that has issues).This is the issue: unstable tcp connections. When you try to ssh to it it just drops the connection, second time does work sometimes. When working in the ssh session you get disconnected randomly.

What I have done so far:
- upgraded all ubuntu's to latest 12.04 LTS
- disabled ipv6
- checked routing on .207 -> just has a default route to our firewall, routing is not the issue as this happens locally.
- checked arp = ok
- rebooted the machines -> issue is the same

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- iptables -L is empty so i guess it's disabled?
- it's a local connection so no it does not pass a firewall (only a default gateway) and i'm testing from same subnet
- tcp_Sack = 1
- tcp_Windows_scaling = 1